<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>responsive-layout-sidebar</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        .container {
            display: grid;
            grid-template-columns: 1fr minmax(150px,20%);
            height: 100px;
        }
        .main,.aside {
            padding: 12px;
            text-align: center;
            color:#fff;
        }
        .main {
            background-color: #eb7d16;
        }
        .aside {
            background-color: #1e4fee;
        }
    </style>
</head>
<body>
    <div class="container">
        <main class="main">
            This element is 1fr large.
        </main>
        <aside class="aside">
            Min: 150px / Max: 20%
        </aside>
    </div>
</body>
</html>